The Black Dog X form magazines are constructed from glass filled nylon with stainless steel feed lips and have a capacity of 25-rounds. The feed lips are lost wax cast from stainless steel and are interchangeable. The magazine is easily disassembled for cleaning and maintenance. The translucentpolycarbonate allows you to see how much ammunition is remaining in the magazine. They are compatible with Atchison, Ciener, CMMG, Spikes Tactical, Tactical Solutions, and Target Master Conversion kits and uppers. These magazines also work with Sig 522, and Kel-Tec PLR22 firearms.